In Mexico there are a lot of stray dogs living on the streets. They are often (but not always) very thin, sickly-looking, and usually scared of people. In the U.S. there are very few stray dogs. There are a lot of animal shelters and if someone finds a stray dog, they usually take it to one.
In the U.S. there are a lot of people living on the streets. They are often (but not always) sickly-looking, and either mentally ill or substance abusers. In Mexico there are few (if any)* people living on the streets. If someone is mentally ill or a substance abuser their family generally takes care of them. If someone is too poor to rent an apartment, they can find some unused bit of land somewhere and build a house out of scrap wood.
In the U.S. you can buy food in supermarkets, farmer's markets, and small stores which are usually crappy and/or expensive. In Mexico you can buy food in supermarkets, mercados (which are kind of like farmer's markets except that they're more permanent and usually much bigger), tianguis (large mercados that happen once a week in a particular area), and small stores which are usually crappy and/or expensive.
In Mexico, the infrastructure (garbage collection, water delivery, etc.) is based on the assumption that someone (usually grandma) will always be home, so nothing needs to be scheduled for an exact time. In U.S. the infrastructure is based on the assumption that no one will be home unless specific arrangements are made.
*I've been in Oaxaca for two months and have yet to see anyone who is homeless. I have seen a few homeless people in other parts of Mexico.
And here's a photo, just because every blog entry should have a photo. This is a tapete, a hand-woven wool rug.